Many of the reasons listed above land on the plus side of my list as well. One of my favs though, is the look on the face and the response of the coworkers when they ask that "you rode your bike today?". In their mind something was extremely uncomfortably. Heat/humidity, rain, snow, wind, or even the threat of something they deem terrible. When in fact, the mornings ride was maybe the most comfortable of the week! Cool early mornings or, just the right layers of clothing when it's cold or, other factors that make a commute enjoyable and your surprised, delayed response is something like "uhhh...yeah, why not?"